1. Technical Field of the Invention
The present invention relates to thermosetting resin compositions for build-up method. More precisely, it relates to thermosetting resin compositions for build-up method comprising an epoxy resin, a curing agent for epoxy resin, and poly(ether sulfone). In addition, it relates to insulating materials for build-up method and build-up print circuit board using said thermosetting resin composition.
2. Description of the Related Art
In recent years, a high-density mounting has been demanded as the progress of downsizing, light weighing and thin shaping of electronic apparatuses. By this reason, it has become required in print circuit board not only to minimize circuit patterns but also to reduce diameter of through holes and via holes, and to adopt blind via holes. Increasing attention has been given to build-up print circuit boards obtainable by the build-up method as a product meeting with these requirements. Practical insulating materials for build-up circuit board include a photo-sensitive resin type having merit that a number of via holes, can be formed in one operation by exposure-development step and a thermosetting resin type which allows formation of finer via holes, by using the laser process. In case of photo-sensitive resin type insulating material, there is a limitation in selection of the photo-sensitive resin which gives a photosensitivity to the resin composition thereof, and there are many know-hows in the exposure-development step. Thus, at present, the thermosetting resin type insulating material is attracting more attention.
Proposed thermosetting resin compositions for use in the thermosetting resin type insulating materials include, in addition to a composition comprising a thermosetting resin alone such as an epoxy resin, a phenoxy resin or the like, a composition comprising a thermosetting resin and a thermoplastic resin. For example, JP-A-7-33991 and JP-A-7-34048 describe a thermosetting resin containing an epoxy resin and a poly(ether sulfone).
When the conventional thermosetting resin composition is used, however, it has been difficult to obtain an insulating material for build-up method which is satisfactory in low-thermal expansion and low-water absorption.